In the oil and gas industry it is often desirable to stimulate a hydrocarbon formation by hydraulically fracturing the formation. This fracturing occurs by pumping a slurry having a proppant, such as sand, bauxite, walnut shells, or the like down a well bore, through perforations therein and into the hydrocarbon producing formation. The proppant remains in the fracture after the fluid has been withdrawn, thus "propping" the fracture open, and enhancing production.
A proppant material moving system, such as a conveyor belt, is used to transfer the proppant (usually sand) from transport and storage containers, or the like to a blender wherein the proppant is mixed with a fluid to form the slurry to be pumped down the well. The present invention is an improved system for automatically matching the quantity of proppant being retreived from the storage containers with the quantity of proppant, required by the blender in order to maintain a desired sand concentration.
Presently, an operator must monitor the quantity of sand being conveyed along a belt, from the storage containers or hoppers, and manually regulate the size of the opening through which proppant feeds onto the belt. Generally, the belt speed is set at its maximum rate of travel and the material feed rate is varied.
U.S. Pat. No. 4,219,133 to Sinsky shows a storage level monitor which uses a weight lowered into a bin as a probe and correspondingly turns on, or shuts off a material feed conveyor. U.S. Pat. Nos. 4,170,311 and 3,935,970 to Spaw illustrate level measuring systems for grain which use a reactance probe to determine material level in a bin and turns on, or shuts off a delivery system based upon the material level. A variable speed delivery system is shown in U.S. Pat. No. 3,724,720 to Bullivant which varies the delivery of material when a constant amount of material is being utilized by a process.